COCRYSTALS OF THE DNA-BINDING DOMAIN OF PHAGE-434 REPRESSOR AND A SYNTHETIC PHAGE 434 OPERATOR

The amino-terminal domain of the phage 434 repressor forms cocrystals with a synthetic phage 434 operator. The cocrystals diffract to at least 4 .ANG., and X-ray crystallographic analysis of them is in progress. An analysis of the packing in the cocrystals shows that complexes consisting of dimers of amino-terminal domain bound specifically to operators are stacked end to end in long protein-DNA rods parallel to the unit cell body diagonals. The DNA in the complexes has 10.5 base pairs/turn and a rise per base of 3.26 .ANG., values consistent with B-form DNA, indicating that DNA is neither unwound nor overwound by bound repressor. The packing analysis suggests an approach that might facilitate the cocrystallization of other DNA-binding proteins with the DNA they recognize.